The present invention relates to a bistable, electronically controlled valve actuator where the motive power for an engine valve is provided by high pressure hydraulic fluid.
Internal combustion engine valves are almost universally of a poppet type which are spring loaded toward a valve-closed position and opened against the spring bias by a rotating cam which is synchronized with the engine crankshaft to achieve opening and closing at fixed times in the engine cycle. This fixed timing is a compromise between the timing best suited for high engine speed and the timing best suited to lower speeds including idling. Power and efficiency are likewise compromised.
The prior art has recognized numerous advantages which might be achieved by replacing cam actuated valve arrangements with other types of valve mechanisms which could be controlled as a function of engine speed, crankshaft position, and other engine parameters. For example, U.S. Pat. No. 4,009,695 discloses hydraulically actuated engine valves each controlled by an intake pintle valve and an outlet pintle valve having respective solenoids which in turn are controlled by a dashboard computer which monitors a number of engine operating parameters. This patent recites many advantages which could be achieved by such independent valve control, but is not able to achieve these advantages due to the slow acting nature of its hydraulics Further, since the patented arrangement attempts to control the valves on a real time basis, the overall system is one with feedback and thus subject to oscillatory behavior.
U.S. Pat. No. 4,945,870, which is hereby incorporated by reference, is entitled VEHICLE MANAGEMENT COMPUTER and discloses a computer control system which receives a plurality of engine operation sensor inputs and in turn controls a number of engine operating parameters including ignition timing, valve timing, and fuel-air mixture. This patent teaches numerous operating modes or cycles in addition to the conventional four stroke cycle, and summarizes numerous prior art schemes for electronic control of engine valves. These schemes include, inter alia, valves which are pneumatically powered and pneumatically or magnetically latched. Magnetic latching may be by solenoids or by permanent magnets which are subjected to an opposed electromagnetic pulse to achieve release. U.S. Pat. No. 4,899,700 discloses control valves and latching plates which are separate from the working piston on the main valve, which results in lower latching forces and reduced mass, resulting in faster operating times.
U.S. Pat. No. 4,974,945, which is hereby incorporated by reference, is entitled ELECTRO-HYDRAULIC VALVE ACTUATOR and discloses a hydraulically powered, electronically controlled valve actuator including a main shaft having a working piston reciprocable in a cylinder defined by a ported sleeve fixed in a housing. A tubular control valve located radially intermediate the sleeve and also having ports is reciprocable to control access between high and low pressure sections of an adjacent reservoir of hydraulic fluid, and the opposed working surfaces of the piston. The control valve is latched by permanent magnets and released by a pulsed electromagnetic field that opposes the permanent magnets.
While U.S. Pat. No. 4,974,945 achieves adequate response times by reducing the length of the fluid paths between the reservoir and the cylinder, it is rendered complex by the presence of springs and pistons in the fluid reservoir and additional springs which provide the motive force for the control valve.